Treatment of acidic raw water using anoxic limestone system

Abstract

Sg. Bekok serves as an important water supply resource for the district of Batu Pahat. In recent years, the water supply intakes within Batu Pahat district have been unable to provide sufficient supply of raw water which has lead to water shortages problem. This was due to water quality deterioration undergone by Sungai Bekok that is highly acidic with low pH values and high acidity. Limestone has been widely used in the treatment of acidic water due to its capability of neutralizing acid and removing metals in water. This study investigated the efficiency of limestone treatment in treating acidic water within a laboratory scale anoxic limestone drain. The anoxic limestone drain was basically designed to enhance limestone dissolution and alkalinity generation thus minimizing the potential of armouring which may decrease the rate of acid neutralization. Actual raw water from two different locations within Sg. Bekok catchment was used in the experiment treated by 30 mm diameter of 112 kg of limestone. The condition under which the pH increases, acidity decreases, alkalinity produced and metals removed in the anoxic limestone drain has been determined in comparison to open limestone channel performance. pH was significantly increased from initially 3.27-4.09 to 6.49-6.67 after flowing through the anoxic drain in 10 minutes of contact with the limestone. Acidity was reduced from 73-99 mg/L as CaCO3 to 17-19 mg/L as CaCO3 as pH were raised to reach near neutral levels. Iron and aluminium were also removed in the anoxic limestone drain. Anoxic limestone drain was found to perform better than the open limestone channel.